There are several ways a web page can store data on a user’s device:
- Web SQL
Here is a light-weight tool that you can use to inspect the cookies and HTML5 web storage data (localStorage and sessionStorage) stored by a web page. You can easily check if a website stores your credit card information in a cookie! The tool can also aid in debugging web pages that store offline data.
To use the tool, simply drag the link (bookmarklet) below to your bookmarks toolbar and invoke it (by clicking on it) when you are on any web page.
To see the tool in action, click the “Offline Data” link above to examine the data stored by this web page.
The tool has no dependencies (such as jQuery) and works in all modern browsers, on both http: and https: web pages.
If your actions on the web page cause changes to the stored data, you can invoke the bookmarklet again, to see the updated data. You can also remove cookies or web storage data by clicking the “X” icon that shows up on hovering on individual items (or section headings).
A future version of the tool will automatically watch cookies and web storage data for changes as well as allow you to edit them inline.
This tool is also available as a Google Chrome Extension.
Offline data stored by google.com:
Offline data stored by builtwithbootstrap.tumblr.com:
Offline data stored by twitter.com: